Since you don't want to take her to the vet for vitals, I think you should switch rolls with the animals. Give the cat the rule of the roost and freedom to explore her new environment. 2 days locked in a bathroom is not going to help the situation. She basically went from trapped to trapped. I...
Well that would be quite the hunger strike if she did! A cat that you've owned for awhile suddenly not eating is always a health issue. But since she's new to your house there are other factors. Do you have other pets in the house? How old is she? Where are you keeping her? As far as the vet...
Obviously the vet would be the best option. We can all give you a bunch of encouraging scenarios that the cat is just scared and will come around soon, but if you trapped it to give it a forever home, a trip to the vet is a must regardless! Best of luck 🐱